Historically, older versions like were sold with permanent serial numbers or CD keys. However, Adobe discontinued these "perpetual licenses" years ago. Today, the software is accessed through the Adobe Creative Cloud platform.
A CD key, also known as a product key, is a unique alphanumeric code used to activate and validate a software product. In the past, software applications, including Adobe Creative Suite (the predecessor to Creative Cloud), required a CD key to install and use the software.